(1) Field of the Invention
The present invention relates to a thermal type ink-jet head for recording an image on a recording medium by ejecting ink droplets from an ejection nozzle by the pressure rise occurring when bubbles arise in the ink which is heated by a heating element.
(2) Description of the Prior Art
As the recording head used in a printer for forming an image on a recording medium, thermal type ink-jet heads have been used which eject ink droplets from an ejection nozzle by the pressure rise occurring when bubbles arise in the ink which is heated by a heating element. In a thermal type ink-jet head, a pulse current is supplied to a heating element arranged on the substrate in accordance with the image data, the heating element heats so that the ink being in contact with the heating element is heated giving off bubbles. Generation and expansion of the bubbles causes pressure rise, whereby ink in the ejection nozzle is ejected out as ink droplets. This ink droplet jumps to the recording medium placed in proximity to the ejection nozzle, creating a recording dot in an image as a recording pattern.
In the thermal type ink-jet head, part of the heat generated from the heating element dissipates by way of the substrate. Therefore, in order to eject a sufficient amount of ink for image forming on the recording medium, a large amount of current needs to be supplied to the heating element, giving rise to a drawback of the electric power consumption being increased.
Japanese Patent Application Laid-Open Hei 7 No.227968 discloses a configuration in which a space as a thermally insulating layer is formed between a heating element (heater) and a substrate so that heat arising from the heating element will not transfer to the substrate.
Japanese Patent Application Laid-Open Hei 2 No.3054 discloses a configuration in which a pressure generating means composed of a vibration plate and a heating layer is provided in the form of a cantilever structure or a simple beam supported at both ends and an electric current is supplied to the heating layer so as to cause a heat distortion within the pressure generating means and thereby deform and displace the pressure generating means in the nozzle plate direction, thus causing ink droplets to jump outside.
Registered Japanese Patent publication No.2769447 discloses a configuration in which two layers having different thermal conductivities are formed between a heating element and a substrate so as to inhibit thermal transfer from the heating element to the substrate.
However, since, with the above ink-jet head, heat arising from the heating element is hard to be released to the exterior, the heat generated while the heat element is energized remains in the heating element after removal of the electric supply. Therefore, even if the current is supplied in pulses to the heating element, the heat builds up in the heating element, elevating the temperature of the heating element, thus causing an overheated state. In this way, the ink-jet head has the drawback of overheating which will lower the response of the heating element, resulting in deficiency in the exact control of the ejected amount of ink.
In the configuration disclosed in Japanese Patent Application Laid-Open Hei 2 No.3054, since the pressure generating member is of a cantilever structure or of a beam supported at both ends, the pressure acting on the ink varies depending upon the positions along the beam, presenting poor ink ejection efficiency.
It is therefore an object of the present invention to provide an ink-jet head which can efficiently heat the ink with heat generated from a heating element while the voltage is applied and hence can reduce the electric power consumption and which can reduce the temperature of heating element rapidly while the voltage is not applied, whereby it is possible to exactly control the ejected amount of ink by making the response frequency of the heating element substantially equal to the frequency of the pulse voltage to be applied to the heating element, thus improving the ink ejection response to the print data.
As the means for solving the above drawbacks, the present invention is configured as follows:
In accordance with the first aspect of the present invention, an ink-jet head for ejecting ink by heating and bubbling ink, includes: a heating element to which electric current is supplied so as to heat and bubble the ink; and a head substrate having a void formed between the heating element and the head substrate, and is characterized in that the heating element will buckle into the void by thermal expansion accompanying the temperature rise thereof.
In accordance with the second aspect of the present invention, the ink-jet head having the above first feature is characterized in that the heating element comprises: a heater; a protective film for protecting the heater; and an insulation film for insulating the heater and the above components are formed of materials having approximately equal coefficients of linear expansion to each other.
In accordance with the third aspect of the present invention, the ink-jet head having the above first feature is characterized in that the heating element is arranged with its movement constrained at both ends with respect to the direction of the thickness and the direction perpendicular to the thickness.
In accordance with the fourth aspect of the present invention, the ink-jet head having the above first feature is characterized in that the heating element is configured so as to come into contact with the head substrate when buckled into the void.
In accordance with the fifth aspect of the present invention, the ink-jet head having the above first feature is characterized in that the void is arranged so as to communicate with a cavity that stores ink.
In accordance with the sixth aspect of the present invention, the ink-jet head having the above first feature is characterized in that the head substrate has a communication hole for establishing communication between the void and the exterior.
In accordance with the seventh aspect of the present invention, an ink-jet head for ejecting ink by heating and bubbling ink, includes: a heating element to which electric current is supplied so as to heat and bubble the ink; and a head substrate having a void formed between the heating element and the head substrate, and is characterized in that the heating element is provided in a bimetal configuration made up of multiple kinds of metals so as to cause the heating element to deform into the void by the temperature rise thereof.
In accordance with the eighth aspect of the present invention, an ink-jet head for ejecting ink by heating and bubbling ink, includes: a heating element to which electric current is supplied so as to heat and bubble the ink; and a head substrate having a void formed between the heating element and the head substrate, and is characterized in that the heating element is formed with a shape memory alloy layer which will deform into the void when the heating element exceeds a predetermined temperature.
In accordance with the ninth aspect of the present invention, an ink-jet head for ejecting ink by heating and bubbling ink, includes: a heating element to which electric current is supplied so as to heat and bubble the ink; a head substrate having a void formed between the heating element and the head substrate; and a piezoelectric actuator which pushes and deforms the heating element toward the void.
In accordance with the tenth aspect of the present invention, an ink-jet head for ejecting ink from a nozzle by heating and bubbling ink, includes: a first substrate; a second substrate arranged opposing the first substrate, defining a space to be filled with ink in corporation with the first substrate; and a heating element disposed between the first and second substrates and having a voltage selectively applied thereto so that the ink inside the space is heated and bubbled, and is characterized in that the heating element is arranged between the first and second substrates with clearances from both, and the heating element comes closer to or in contact with the first or second substrate by elastic deformation occurring from thermal stress during heating.
In accordance with the eleventh aspect of the present invention, the ink-jet head having the above tenth feature is characterized in that the elastic deformation is elastic buckling that occurs when the temperature of the heating element reaches the predetermined temperature.
In accordance with the twelfth aspect of the present invention, the ink-jet head having the above tenth feature is characterized in that the first or second substrate has an opposing surface which allows area contact with the heating element when it is elastically deformed.
In accordance with the thirteenth aspect of the present invention, the ink-jet head having the above tenth feature is characterized in that the heating element is provided in the form of a plate that is fixed at both ends with respect to at least one direction within the surface thereof opposing the first or second substrate.
In accordance with the fourteenth aspect of the present invention, the ink-jet head having the above thirteenth feature is characterized in that the heating element is provided in the form of a plate that is fixed at the entire periphery of the surface thereof opposing the first or second substrate and held between the first and second substrates.
In accordance with the fifteenth aspect of the present invention, the ink-jet head having the above tenth feature is characterized in that the heating element elastically deforms by thermal stress arising at a temperature approximately equal to the bubbling temperature of the ink.
In accordance with the sixteenth aspect of the present invention, the ink-jet head having the above tenth feature is characterized in that the heating element has been previously given an internal stress causing compression with respect to one direction within the surface thereof opposing the first or second substrate.
In accordance with the seventeenth aspect of the present invention, the ink-jet head having the above tenth feature is characterized in that the heating element is provided in the form of a plate having a multi-layered configuration in which an internal stress has been previously given so as to determine the direction of elastic deformation when the heating element heats.
In accordance with the eighteenth aspect of the present invention, an ink-jet head for ejecting ink includes: an ejection nozzle for ejecting ink: an ink chamber arranged in communication with the ejection nozzle; and a heating element disposed in the ink chamber, which gives off bubbles by heating the ink in contact with the heating element by selective activation and causes ink ejection from the ejection nozzle making use of the pressure arising when the bubbles expand, and is characterized in that the heating element elastically deforms toward the ink chamber when it reaches the predetermined temperature.
In accordance with the nineteenth aspect of the present invention, the ink-jet head having the above eighteenth feature is characterized in that a void is formed below the heating element.
In accordance with the twentieth aspect of the present invention, the ink-jet head having the above nineteenth feature is characterized in that the void is made in communication with the exterior.
In accordance with the twenty-first aspect of the present invention, the ink-jet head having the above eighteenth feature is characterized in that the heating element abuts the surface of the ink chamber opposing the heating element when the heating element reaches the predetermined temperature.
In accordance with the twenty-second aspect of the present invention, the ink-jet head having the above twenty-first feature is characterized in that the ink chamber has an opposing surface which opposes the heating element so as to allow area contact with the heating element when the heating element is elastically deformed.
In accordance with the twenty-third aspect of the present invention, the ink-jet head having the above eighteenth feature is characterized in that the heating element has a multi-layered configuration in which the outermost layer facing the interior of the ink chamber has been previously given an internal stress causing compression.
In accordance with the twenty-fourth aspect of the present invention, the ink-jet head having the above eighteenth feature is characterized in that the heating element is fixed at the entire periphery thereof to the bottom face of the ink chamber.
In accordance with the twenty-fifth aspect of the present invention, the ink-jet head having the above eighteenth feature is characterized in that the heating element is of an approximately circular shape.
In accordance with the twenty-sixth aspect of the present invention, a fabrication method of an ink-jet head, includes the steps of: forming an void-forming material and a heating element on the top of a first substrate, in this sequential order; removing the void-forming material; and arranging a second substrate a predetermined distance away from the top surface of the heating element.
In accordance with the twenty-seventh aspect of the present invention, the fabrication method of an ink-jet head having the above twenty-sixth feature is characterized in that the formation of the heating element includes an electrolytic plating step with such a current density that the plated layer will have an internal stress causing compression.
In accordance with the twenty-eighth aspect of the present invention, the fabrication method of an ink-jet head having the above twenty-sixth feature is characterized in that the formation of the heating element includes electrolytic plating steps using different current densities.
According to the above first configuration, heat diffusion from the heating element is prevented by the insulating effect of the void when ink is heated, enabling its sharp temperature rise. After ink ejection, the heating element buckles so that heat from the heating element is released through the head substrate to lower the temperature of the heating element rapidly.
In the above second configuration, it is possible to prevent occurrence of cracks due to repeated heat cycles.
In the above third configuration, it is possible to positively cause the heating element to buckle toward the void.
In the above fourth configuration, heat from the heating element can be well dissipated through thermal conduction via its contact with the head substrate.
In the above fifth configuration, the ink functions as the heat transfer medium when the heating element release heat thus improving the heat transfer to the head substrate and hence enabling beneficial heat radiation.
In the above sixth configuration, heat inside the void can be released outside through the communication hole.
In the above seventh, eighth and ninth configurations, it is possible to positively perform deformation of the heating element into the void.
In the above tenth configuration, the heating element arranged out of contact with the first and second substrates elastically deform by thermal stress during heating into contact with the first or second substrate. Therefore, the heat generated in the heating element will not dissipate through the substrate while the heating element heats, thus making it possible to efficiently heat the ink in contact with the heating element. On the other hand, heat remaining in the heating element after the completion of heating of the heating element will be dissipated through the first or second substrate in contact, thus making it possible to cool down the heating element quickly.
In the above eleventh configuration, the heating element quickly deforms by elastic buckling when the heating element reaches the predetermined temperature. Therefore, the heating element can be set quickly closer to or brought into contact with the first or second substrate in response to the temperature change.
In the above twelfth configuration, the heating element which has elastically deformed by its own heat comes into area contact with the first or second substrate. Therefore, a large amount of heat can be released from the heating element through the first or second substrate in contact, thus making it possible to cool down the heating element quickly.
In the above thirteenth configuration, the heating element is fixed at both ends with respect to at least one direction within its surface opposing the first or second substrate so that the heating element will not be moved at both ends by thermal deformation during heating. Therefore, the mid part of the heating element moves closer to or into contact with the first or second substrate by the elastic deformation arising during heating.
In the above fourteenth configuration, the heating element is fixed at the entire periphery of its surface opposing the first or second substrate and held between the first and second substrates so that the heating element will not move at the periphery thereof by thermal deformation during heating. Therefore, the central part of the heating element moves closer to or into contact with the first or second substrate by the elastic deformation arising during heating.
In the above fifteenth configuration, the heating element moves closer to or brought into contact with the first or second substrate by elastic deformation when the ink has been heated approximately close to the bubbling temperature. Therefore, the heating element cools down by the heat radiation of the first or second substrate immediately after the ejection of bubbling ink from the nozzle.
In the above sixteenth configuration, the heating element before heating has been previously given a residual stress causing compression with respect to one direction within the surface thereof opposing the first or second substrate. Therefore, the heating element elastically deforms in a reliable manner by the thermal stress arising in the compressing direction during heating.
In the above seventeenth configuration, the heating element is provided in the form of a plate having a multi-layered configuration in which an internal stress has been given previously in its unheated state so as to determine the direction of elastic deformation when the heating element heats. Therefore, the heating element will positively deform in the predetermined direction when it is heated.
In the above eighteenth configuration, the heating element for heating the ink and giving off bubbles in order to eject the ink from the ejection nozzle will elastically deform toward the interior of the ink chamber when it is activated and reaches the predetermined temperature.
Therefore, the pressure arising when bubbles expand and the pressure arising when the heating element elastically deforms act on the ink and hence the ink droplets can be ejected outside the ink-jet head by the combined pressure. This configuration contributes to reduce the current to be supplied to the heating element to bubble the ink, thus making it possible to reduce the power consumption.
In the above nineteenth configuration, the void is formed below the heating element provided in the in chamber. This void functions as the insulation layer when the heating element heat by supplying a pulse of current. Therefore, heat diffusion from the heating element to the substrate can be inhibited, thus enabling sharp temperature rise of the heating element.
In the above twentieth configuration, the void provided below the heating element is put in communication with the exterior. Therefore, it is possible to prevent reduction in the pressure in the void, which enables smooth elastic deformation of the heating element.
In the above twenty-first configuration, when the heating element is heated and reaches the predetermined temperature by supplying electric current, the heating element elastically deforms by thermal stress and comes into contact with the surface of the ink chamber opposing the heating element. Therefore, heat arising in the heating element is released through the abutment of the heating element with the surface of the ink chamber opposing the heating element, thus making it possible to cool the heating element quickly after the generation of bubbles. As a result, an improved heating and cooling response to the selectively activated pulse current can be achieved, thus making it possible to control the ejected amount of ink with high precision.
In the above twenty-second configuration, the heating element having been elastically deformed by heating comes into area contact with the opposing surface which opposes the heating element. Therefore, the heating element can be brought into contact with the surface opposing the heating element through an enlarged area, thus improving the heat radiation efficiency and enabling rapid cooling of the heating element.
Further, in this configuration, the surface of the ink chamber opposing the heating element is made of metal. That is, the heating element which has been elastically deformed by its heating abuts or comes closer to the metal-made opposing surface of the ink chamber, the heat arising in the heating element can be released quickly.
According to the above twenty-third configuration, in the heating element having a multi-layered configuration, the outermost layer facing the interior of the ink chamber has been previously given an internal stress causing compression. Therefore, the heating element will always deforms elastically in the fixed direction when the heating element is heated by supplying current and reaches the elastically deforming temperature.
In the above twenty-fourth configuration, the heating element provided in the ink chamber is fixed at the entire periphery thereof to the bottom face of the ink chamber. Therefore, it is possible to positively deform the heating chamber towards the interior of the ink chamber when it elastically deforms from heating. No leakage of ink from the periphery of the heating element will occur when the elastic element elastically deforms.
In the above twenty-fifth configuration, the heating element arranged in the ink chamber is formed in an approximately circular shape. This configuration provides large displacement of the heating element when it is elastically deformed, compared to other shapes having the same area. Therefore, it is possible to apply a greater pressure on the ink in the ink chamber.
In the above twenty-sixth configuration, a void can be formed between the heating element and the first substrate by removing the void-forming material from the top surface of the first substrate after the formation of the heating element. Therefore, it is possible to easily fabricate an ink-jet head having a void between the first substrate, and the second substrate and the heating element.
In the above twenty-seventh configuration, the heating element is formed as a plated layer by electrolytic plating so as to previously give an internal stress causing compression to the heating element. That is, the heating element during heating receives internal stress acting in the compressive direction, in addition to the thermal stress due to heating. Accordingly, the temperature for causing the heating element to deform into the predetermined shape when heated can be lowered.
In the above twenty-eighth configuration, the heating element is formed by electrolytic plating using different current densities which affect the internal stresses to be given to the plated layers. That is, multiple layers having different internal stress states can be formed. Therefore, it is possible to provide an ink-jet head having a heating element which deforms in a univocal direction determined by the stress states of the individual layers inside the heating element when thermal stresses arise due to heating.